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AR# 7939

Virtex I/O - Users can specify that unused pins can be tied high, low, or left floating


By default, unused I/O pins on a Virtex device will have their weak pull-down resistors activated (~ 50k-100k ohms to ground). In 3.1i Alliance and Foundation software, the user can instead specify that unused I/Os be either pulled up or left floating. This is accomplished through a hidden BitGen setting.


Instructions for changing this setting in the different software tools follow. Please note that this setting will not be listed in the BitGen report. In addition, there is no way to change this setting after the device is configured.


1. From the Project Manager, access the Implementation Template Manager through Tools -> Utilities.

2. Select "Configuration Templates."

3. While highlighting "Default," select "Customize."

4. Under "Program Options," specify one of the following, then click "Set":

-g unusedpin:pullup

-g unusedpin:pulldown

-g unusedpin:pullnone


1. From the Design Manager, select Utilities -> Template Manager.

2. Follow the instructions above.

Foundation ISE:

1. After running through the implementation flow once, select Create Programming File -> View Programming File Generation Report.

2. In this report, you will find the BitGen command line. Copy and paste it into a command shell, adding one of the above "-g" options to the command.

3. Rerun BitGen.

No option for this is currently available in Foundation 4.1i. (A CR is pending.)
AR# 7939
Date Created 08/21/2007
Last Updated 04/24/2012
Status Archive
Type General Article